The apparatus of the present invention was developed as an improvement of the structures disclosed in McGee, Et Al Subsurface Gate Valve Safety Device, Ser. No. 794,020, now abandoned, for use in certain cases. It is intended by this reference to incorporate the disclosure of said prior application in this document.
In the gate valve of the aforesaid McGee, Et Al application, longitudinal motion of a remotely actuated operator was converted to transverse sliding of a gate by the cam-like internal Z-legged web of the hydraulic operator sliding against a part of the gate. With experience it was found that the sliding action resulted in excessive wear, due to the relatively great force level needed for effecting the sliding. The operator piston was exposed to well pressure; typically the operating pressure was at least or about 1.2.times.well pressure (e.g. 12,000 p.s.i.).